U.S. Pat. Nos. 3,808,178 and 4,120,570, issued to N. E. Gaylord in 1974 and 1978 respectively, concerns linear random copolymers of polysiloxanyl and alkyl acrylates and methacrylates which have increased oxygen permeability, as compared to the alkyl methacrylates alone for example. Use of the polymers in contact lenses for correcting visual defects of the human eye is taught. Further modifications of such polymers with an itaconate ester, and preferably including a crosslinking agent and a hydrophilic monomer, are disclosed in U.S. Pat. No. 4,152,508 issued to E. J. Ellis et al. (1979).
U.S. Pat. No. 4,254,248 issued to G. D. Friends et al. (1981) concerns acrylate and methacrylate soft contact lenses using as a comonomer polysiloxanes end-capped with polymerizable unsaturated groups. The copolymers have high tear strengths and a high modulus of elasticity. Such comonomers are also disclosed in U.S. Pat. No. 4,189,546 issued to W. G. Deichert et al. (1980) to make polymeric shaped articles for biomedical applications.
U.S. Pat. No. 3,786,116, issued to R. Milkovich et al. in 1974 discloses the use of macromonomers containing a polymerizable carbon-carbon double bond to make graft copolymers comprising a backbone polymer chain and bonded thereto a linear polymer which forms copolymerized sidechains on the backbone. In other words, the macromonomer is interposed between polymeric segments of the backbone polymer.
In the prior art, as represented for example by the above Gaylord patents, improvements in one polymer property by copolymerization, such as oxygen permeability, are frequently gained at the expense of another property, such as hardness or machineability. Optical clarity must remain unaffected as well. Improved methods and materials which can provide polymeric contact lens compositions having improved combinations of properties remain highly desirable.
An object of this invention is a novel acrylic block copolymer or macromonomer which is compatible with and can be used as a constituent in polymer compositions for contact lenses to provide improved properties. Another object is a novel macromonomer which can be incorporated into polysiloxanyl-, alkyl-(meth)acrylate copolymers (i.e. soluble in the other monomers) during bulk polymerization of the comonomers to provide a branched copolymer having a novel combination of oxygen permeability and hardness while not adversely affecting optical clarity.